Helical barbed tape is used to create an elongated antipersonnel barrier. The helical barbed tape is defined by an elongated generally flat central support having clusters of barbs at spaced apart locations. Each cluster of barbs typically will comprise a first pair of barbs extending from a root on one side of the tape and a second pair of barbs extending from a root on the opposite side of the tape. Each barb is a generally elongated planar structure having two generally opposed edges converging toward one another and meeting at a very sharp point. The barbs in each pair lie in a common plane, but extend in generally opposite directions relative to one another. Furthermore, each pair of barbs is offset relative to the plane of the central supporting portion of the tape such that one barb in each pair extends angularly away from one surface of the central support while the other barb in that pair extends angularly away from the opposite surface of the central support. To achieve optimum effectiveness, the first and second pairs of barbs are offset in opposite angular directions. Thus, when the tape is viewed from its side, each cluster of barbs effectively defines an X.
The above described barbed tape is formed into a helical configuration such that the plane of the tape is aligned generally perpendicular to the axis of the helix. Thus, the points of the barbs extend in generally tangential directions relative to the helix, while the roots to which the pairs of barbs are joined extend in generally radially outward or radially inward directions relative to the helix. One preferred method for forming the above described helical barbed tape is described in U.S. patent application Ser. No. 876,715 which was filed on June 20, 1986 by John W. Mainiero, and which is entitled "BARBED TAPE AND APPARATUS AND PROCESS FOR MAKING SAME." Another method for forming the above described helical barbed tape is shown in U.S. Pat. No. 4,028,925 which issued to Michael R. Mainiero on June 14, 1977.
The helical barbed tape described above can be axially collapsed for shipment and storage such that each coil of the helix directly abuts the adjacent coil. However, the helical barbed tape is stretched out a preselected amount during deployment.
The above described helical barbed tape has a broad range of both private and governmental applications, all of which relate to security. In the typical private application, the helical barbed tape is mounted to the top of a fence or wall to prevent the fence or wall from being scaled by an intruder. A particularly prevalent private application consists of a single strand of the helical barbed tape mounted to the top of a chain link fence. The governmental applications can be considerably more complex depending upon the particular needs. For example, in military applications, one or more strands of the helical barbed tape will be stretched along the ground to define an antipersonnel barrier. In some such applications, it may be desirable to rapidly deploy the helical barbed tape to meet a particular exigency. At prisons and certain high security permanent military installations, several coils of the helical barbed tape may be employed with fences. In these instances, a plurality of coils of the barbed tape may be secured adjacent the base of the fence while one or more coils may be secured at the midpoint or top of the fence. In some of these instances, each coil will effectively define a double helix comprising an external helix generated in a first direction and smaller concentrically disposed internal helix generated in the opposite direction.
The helical barbed tapes are deployed such that a person attempting to pass therethrough will contact at least a portion of the helix. This initial contact often will be with one or more of the closely spaced barbs on the tape, which are formed with sufficient sharpness to inflict a severe wound. This initial contact with the tape will also cause wavelike movements elsewhere on the helical tape causing other barbed clusters to be urged into contact with the intruder. Thus, even if the initial contact with the helical barbed tape is at a location spaced from a barbed cluster, this initial harmless contact is virtually certain to urge other barbed clusters into the intruder.
Although the helical barbed tapes have proved to be much more effective than the older barbed wire concertina, there have been several problems. For example, it has been necessary to form the barbed tape from a material having a thickness sufficient to insure that each barb will be rigid enough to slash into an intruder and to maintain its shape during normal pre-installation handling. To insure the necessary barb strength, the tapes typically have been formed from a stainless steel 0.025 inches thick. The formation of the helical barbed tape from significantly thinner steel would result in barbs that bend in response to the forces exerted by or on the intruder or in response to forces normally encountered during handling, shipment or storage prior to installation. In the typical application, the helical barbed tape is formed from an austenitic stainless steel at least the central portions of which may be hardened to Rockwell 30 N 55. Although this material is expensive, the stainless steel is required to insure that the product will endure when exposed to the elements, and the 30 N 55 hardness of the central supporting portion contributes to the spring characteristics of the coil. The cost of the product is directly proportional to the thickness of the tape. Thus, it would be desirable to provide a tape that is thinner and therefore less costly. However, as explained above, the barbs of the thinner tape would bend too easily, thereby yielding an ineffective product.
The thickness of the steel also directly affects the weight of the helical barbed tape. Heavier products create various storage problems and substantially increase shipping costs. The heavy products also make rapid military deployments difficult. Furthermore, the heavy helical barbed tapes often require additional reinforcement to the fences upon which the coils are mounted.
In addition to these problems of cost and weight, the sharpness of the barb varies inversely to the thickness of the tape. Thus, the rigidity of a thick barb is achieved at the expense of sharpness.
Another aspect of the subject invention is an improved helical barbed tape having barbs with enhanced rigidity, and having electrical sensor means so as to be capable of use in an electronic intrusion detection system to mechanically detect disturbances induced on the barbed tape or its supporting structures, such a fence, wall, post, etc. Heretofore, it has been known to employ a standard chain link or barbed wire fence in combination with a linear length of coaxial cable transducer extending along the length of the fence and capable of producing an alarm when an intrusion or compromise of the fence is attempted. As an example, reference is made to U.S. Pat. No. 3,763,482 entitled "COAXIAL FENCE TRANSDUCER" which issued on Oct. 2, 1973 to Burney et al. In U.S. Pat. No. 3,763,482, a coaxial cable with a dielectric filler comprising a radially polarized electret develops and transmits a signal along the cable in response to deformation of the cable at any point along the length. Such a coaxial cable, when clamped to a chain link, barbed fence or similar fences in a generally straight disposition, generates an electrical signal in response to attempts of intruders to climb or cut the fence and transmits that signal to remote alarm equipment. Standard coaxial cable is modified to form such a transducer by heating the entire cable, applying a dc potential across the ends of the outer and inner conductors, while the dielectric filler is heat-softened, cooling the cable while maintaining the electrical stress on it, and finally removing the bias voltage. Signal amplification and processing electronics, which are connected to the cable, detect intrusions and discriminate against false alarm signals. As shown and described in U.S. Pat. No. 3,763,482, the coaxial cable is secured along the length of the fence by clamping rings. Other forms of known coaxial cables are capable of operating in a similar manner are generally known as piezoelectric transducers and geophone transducers.
Another prior art system is marketed under the trademark "PERISTOP" wire by Bigotec AG of Aaron, Switzerland, and comprises a galvanized hollow steel wire containing an insulated copper conductor, and is installed inside a conventional barbed tape concertina. The resulting PERISTOP barbed tape concertina is designed to respond only to the destruction or cutting through of a wire loop. The response is achieved through the electronic monitoring of interruptions or short circuits in the system.
In view of the above, it is an object of the subject invention to provide a helical barbed tape having barbs with improved rigidity.
It is another object of the subject invention to provide a helical barbed tape having barbs with improved sharpness.
It is an additional object of the subject invention to provide a helical barbed tape that can be formed from a thinner lighter tape while still maintaining sufficient rigidity of the barb.
It is a further object of the subject invention to provide a composite helical barbed tape having barbs with improved rigidity, and having an electrical vibration sensitive cable extending along the length thereof, with the barbed tape being disposed about said electrical cable.